Recently, various portable electronic devices have become widespread, by the rapid development of a miniaturization technology of an electronics device. And miniaturization is also required for batteries which are power sources for these portable electronic devices, and a nonaqueous electrolyte secondary battery having a high energy density has attracted attention.
A nonaqueous electrolyte secondary battery using metal lithium as a negative electrode active material has an extremely high energy density, but since a resinous crystal called dendrite is separated on a negative electrode at the time of charging, battery life is short, and there was also such a problem in safety that dendrite grows and reaches a positive electrode to cause internal short-circuit. Accordingly, as a negative electrode active material for replacing lithium metal, a carbon material to insert/extract lithium, particularly graphite carbon has been used.
In addition, as a negative electrode active material pursuing a further high energy density, an effort has been made to use particularly an element which is alloyed with lithium, such as silicon, tin, or a material having a large lithium insertion capacity and a high density, such an amorphous chalcogen compound. Among them, silicon can insert lithium up to a ratio of 4.4 lithium atoms to 1 silicon atom, and a negative electrode capacity per mass thereof is about 10 times that of graphite carbon. But regarding silicon, change of the volume in accompany with insertion/extraction of lithium in a charge/discharge cycle is large, and there was a problem in a cycle life such as pulverization of active material particles.